1. Field of the Invention
The present invention relates to a nozzle plate for use in an ink jet type print head and a manufacturing process of the nozzle plate, and more particularly to a nozzle plate provided with nozzle orifices through which ink is to be ejected, the orifices being formed by an excimer laser using a working lens having the numerical aperture set in a range of 0.1 to 0.35, and a manufacturing process of the nozzle plate.
2. Description of Related Art
A nozzle plate used in an ink jet type print head is conventionally provided with minute nozzle orifices through which ink droplets can be ejected, the nozzle orifices being formed by a perforating operation with an excimer laser (for instance, ArF=198 nm, KrF=248 nm, XeKr=308 nm) which emits ultraviolet light. For a working lens used in the perforating operation, the working lens having a numerical aperture (NA) being usually about 0.05 has been used.
This numerical aperture (NA) represents an amount of the performance in connection with brightness and resolving power and the like of an optical system. In engineering instruments, if assuming the angle formed by a radius of an entrance pupil with respect to a point-shaped object (object point) on an optical axis as xcex1 and the refractive index of a medium in which the object point exists as xe2x80x9cnxe2x80x9d, the numerical aperture (NA) is represented by n sin xcex1.
Here, FIGS. 7 through 9 show the shapes of nozzle orifices formed in the conventional nozzle plate, which are formed by a working lens having NA=0.5. FIG. 7(a) is a front view of the conventional nozzle plate and FIG. 7(b) is a sectional view of the same. FIG. 8 and FIG. 9 are microphotographs of the nozzle orifices in the conventional nozzle plate.
The conventional nozzle plate 31 is formed of a material having the solution resistance with respect to a solvent included in the constituent of ink to be used, and is provided with many nozzle orifices 32 through which the ink can be ejected as shown in FIG. 7(a). FIG. 7(b) is a sectional view of the conventional plate 31 in the case where the perforating operation is performed on the nozzle plate 31 by irradiating it with a laser beam from above in the figure. As shown in the figure, the sag (round portion) is produced around the nozzle orifice 32 in the nozzle plate 31 by the perforating operation.
Next, the relation between the size of the sag and the numerical aperture (NA) of the working lens as shown in FIGS. 5(a) and 5(b), in which the length L of the sag is defined as an amount of sag L (xcexcm). It is found, as shown in FIG. 5(a), that as the sag amount is smaller, the processing precision is higher. As the conventional nozzle plate is subjected to a perforating operation usually using the working lens the numerical aperture (NA) of which is 0.05, the sag amount becomes about 5 xcexcm as shown in FIG. 5(b). The actual shape of the nozzle orifice formed in the conventional nozzle plate in the above manner is shown in FIGS. 8 and 9 which are microphotographs.
For a nozzle plate, it is generally required to reduce the amount of sag to be produced around the ink ejection orifice into 2 xcexcm or less, which is because a large amount of sag tends to cause the reduction of the speed of ink droplets when ejected and the deflection of ink upon ink ejection, thus resulting in a deterioration in print quality.
Accordingly, in the conventional nozzle plate, a plane thereof on which the laser is incident is adhered to an actuator after the perforating operation. Specifically, the laser incident plane on which sag is produced is adhered to the actuator with an adhesive agent to form a print head in order to raise a processing precision of the nozzle orifice at a side from which ink is to be ejected and thereby to form a stable meniscus of ink. This is because, if the form of the meniscus of ink is unstable, a direction of ink ejecting from the nozzle orifice may become unstable due to a curvature of ink droplet, and variations in the timing of ink ejection may occur, thereby resulting in a deterioration in print quality.
However, there are the following disadvantages in the conventional nozzle plate and the manufacturing process thereof.
The conventional nozzle plate is manufactured such that nozzle orifices are first formed in the nozzle plate by a laser processing operation and, after that, the processed nozzle plate is adhered to an actuator with an adhesive agent. Upon the adhering operation, it is likely that excess adhesive agent flows into the inside of the nozzle orifices. This may cause the nozzle orifices to become unstable in shape and also the meniscus of ink to be unstable. In addition, the nozzle plate is adhered to the actuator after the nozzle orifices are formed, so that it needs to accurately make positioning between the nozzle orifices and the actuator to prevent a positional deflection therebetween. This is because such the positional deflection causes ink ejection in an unstable direction and variations in the timing of ink ejecting. Due to the above disadvantages, an adhering operation requires an extremely high-level and difficult technique.
To the contrary, to prevent the above disadvantages upon the adhering operation, conceivable is a process in which the nozzle plate is first adhered to the actuator and then is subjected to a perforating operation using an excimer laser. In such the case where the perforating operation is performed on the nozzle plate by using an excimer laser after the adhering operation, it is preferable to execute the perforating operation by making a laser beam be incident on a plane of the nozzle plate from which ink is to be ejected. This is because, if the nozzle plate is processed from the side of the plane adhered to the actuator, the energy of the excimer laser incident onto the nozzle plate may weaken the adhesive strength between the nozzle plate and the actuator and deflect the mating position of the nozzle plate and the actuator and, in the worst case, may take the nozzle plate off the actuator.
Accordingly, after the adhering operation, the perforating operation on a nozzle plate is conducted by making the excimer laser be incident onto the plane of the nozzle plate from which ink is to be ejected. In this case, sag is produced on the nozzle orifices at the ink ejecting side, i.e., the surface irradiated by the excimer laser upon the perforating operation. When the perforating operation is performed with the working lens having NA=0.05 as above, the sag amount becomes about 5 xcexcm as shown in FIG. 5(b), which is so large to make a meniscus of ink unstable.
As a result, there are such disadvantages that the ejecting direction of ink ejected from the nozzle orifice becomes unstable due to the curvature of ink droplet, and variations in the timing of ink ejection is produced, resulting in a deterioration in print quality.
As mentioned above, the adhering operation requires a difficult technique when the perforating operation using an excimer laser is performed on the nozzle plate before the nozzle plate is adhered to the actuator, to the contrary, the shapes of the nozzle orifices become unstable when the perforating operation is performed after the adhering operation. Consequently, both ways can not produce a satisfactory processed nozzle plate.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a nozzle plate for an ink jet head provided with nozzle orifices and a manufacturing process of the nozzle plate, capable of reducing sag which will be produced in processing the nozzle plate by an excimer laser device to form the nozzle orifices through which ink can be ejected, of easily adhering the nozzle plate to an actuator and the like, and of forming the nozzle orifices in desired shapes thereby to increase the print quality.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, a nozzle plate for an ink jet head of this invention, provided with nozzle orifices through which ink is to be ejected, is characterized in that the nozzle orifices are formed in the nozzle plate by an excimer laser device with a working lens which has a numerical aperture (NA) set to 0.13 or more and 0.35 or less.
In another aspect of the present invention, the nozzle orifices are formed by the excimer laser device with the working lens which has the numerical aperture set to 0.2 or less.
In further aspect of the present invention, a range of the numerical aperture is determined based on size of sag produced around the nozzle orifice and a focal depth of an optical system used in the excimer laser device.
In still further aspect of the present invention, the lowermost value 0.13 in the range of the numerical aperture approximately corresponds to 2 xcexcm size of the sag.
In still further aspect of the present invention, the uppermost value 0.35 in the range of the numerical aperture approximately corresponds to 1 xcexcm of the focal depth.
In still further aspect of the present invention, the nozzle orifices are formed on a surface of the nozzle plate from which ink is ejected.
In still further aspect of the present invention, the nozzle orifices are formed in the nozzle plate after the nozzle plate is connected with an actuator for ejecting ink through the nozzle orifices.
In still further aspect of the present invention, the nozzle plate is made of material capable of resisting solvent included in ink.
In still further aspect of the present invention, the material is polyimide resin.
In general, a resolving power R by a projective lens and a focal depth D thereof are calculated based on a numerical aperture of an optical system and a wavelength xcex of an exposure light, namely, by the following equations; R=k1xcex/NA, D=xc2x1k2xcex/NA2, where k1 and k2 are constants which are determined depending on materials to be used. Based on the above equations, it is proved that the resolving power R increases in reverse proportion to the NA if the wavelength of the exposure light is fixed, i.e., a processing precision can be made higher by determining the NA larger.
On the other hand, the focal depth D is inversely proportional to NA2. If the NA is increased to make the processing precision higher, the focal depth is reduced, thereby requiring a working technique such as a positioning operation.
The relation between the NA of the optical system and an amount of sag is shown in FIG. 5(b).
If the NA of a working lens to be used in processing nozzle orifices by an excimer laser is set to 0.13 or more, resolving power become better, so that the nozzle orifices can be processed without producing sag therein. As shown in FIG. 5(b), when NA is 0.13, for example, the amount of sag is about 2 xcexcm. In the case where the amount of sag is 2 xcexcm or less, there is no problem in nozzle orifices to be used. It is therefore preferable that the NA is 0.13 or more in view of the amount of sag.
Subsequently, the relation between the NA of the optical system and the focal depth is shown in FIG. 6. If the NA is set to larger, the focal depth is further reduced. When the NA is 0.15, for example, the focal depth becomes about 5 xcexcm. In this way, the reduced focal depth makes the positioning operation in a processing operation more difficult. The focal depth becomes about 1 xcexcm when the NA is 0.35. If the focal depth is further reduced than that value, the positioning operation becomes extremely difficult. It is therefore preferable that the NA is 0.35 or less in view of the focal depth. More preferably, the NA is 0.2 or less at which the focal depth becomes 3 xcexcm or more.
Further, if the NA is set in a range of 0.13 to 0.35, the amount of sag at a laser irradiated plane of the nozzle plate is reduced to the level causing no trouble in use, so that there is no problem in that the laser irradiated plane is used for an ink ejecting plane. Accordingly, after the nozzle plate is adhered to an actuator, a perforating operation can be executed on the nozzle plate by making an excimer laser beam be incident the plane from which the ink is to be ejected. This makes it possible to prevent the disadvantages such as the difficult positioning and the flowing of an adhesive agent into the nozzle orifices upon the adhering operation.
Based on the above points, it is possible to easily form nozzle orifices having clear shapes and make the form of a meniscus stable, so that no variation occur in the ejecting direction of the ink ejected from the nozzle orifices and the timing of ink ejection. Consequently, a print head using the nozzle plate according to the present invention enables to achieve printing with a high print quality.
Furthermore, a manufacturing process of the present invention, for manufacturing a nozzle plate for an ink jet head provided with nozzle orifices though which ink is to be ejected, is characterized in that an excimer laser device with a working lens which has a numerical aperture (NA) set to 0.13 or more and 0.35 or less is utilized for forming the nozzle orifices in the nozzle plate.
In another aspect of the present invention, the excimer laser device with the working lens which has the numerical aperture set to 0.2 or less is utilized for forming the nozzle orifices.
In further aspect of the present invention, a range of the numerical aperture is determined based on size of sag produced around the nozzle orifice and a focal depth of an optical system used in the excimer laser device.
In still further aspect of the present invention, the lowermost value 0.13 in the range of the numerical aperture approximately corresponds to 2 xcexcm size of the sag.
In still further aspect of the present invention, the uppermost value 0.35 in the range of the numerical aperture approximately corresponds to 1 xcexcm of the focal depth.
In still further aspect of the present invention, the nozzle orifices are formed on a surface of the nozzle plate from which ink is ejected.
In still further aspect of the present invention, the nozzle orifices are formed in the nozzle plate after the nozzle plate is connected with an actuator for ejecting ink through the nozzle orifices.
According to the manufacturing process of the present invention, the nozzle plate having nozzle orifices complete in shape can easily be manufactured. Because of the stable form of a meniscus of ink, no variation occur in the ejecting direction of ink to be ejected from the nozzle orifices and the timing of ink ejection. As a result, a print head using the nozzle plate manufactured by the above process according to the present invention can conduct a printing operation with an excellent print quality.